The present invention generally relates to a plasma process and a chamber for conducting such process and more particularly, relates to a method for preventing particle contamination in a plasma process chamber and an apparatus for carrying out such method.
In the fabrication of semiconductor integrated circuit (IC) devices, various device features such as insulation layers, metallization layers, passivation layers, etc., are formed on a semi-conducting substrate. It is known that the quality of an IC device fabricated is a function of the processes in which these features are formed. The yield of an IC fabrication process is in turn a function of the quality of the device fabricated and a function of the cleanliness of the manufacturing environment in which the IC device is processed.
The ever increasing trend of miniaturization of semiconductor IC devices occurring in recent years requires more stringent control of the cleanliness in the fabrication process or in the processing chamber where the process is conducted. This leads to a more stringent control of the maximum amount of impurities and contaminants that are allowed in a process chamber. When the dimension of a miniaturized device approaches the sub-half-micron level, even a minutest amount of contaminants can significantly reduce the yield of the IC manufacturing process. For instance, the yield of the process can be drastically reduced by the presence of contaminating particles during deposition or etching of films which leads to the formation of voids, dislocations or short-circuits resulting in performance and reliability problems in the IC devices fabricated.
In recent years, contamination caused by particles or films has been reduced by the improvements made in the quality of clean rooms and by the increasing utilization of automated equipment which are designed to minimize exposure to human operators. However, even though contaminants from external sources have been reduced, various contaminating particles and films are still generated inside the process chamber during the processing of semiconductor wafers. Some possible sources of contamination that have been identified include the process gases and liquids, the interior walls of the process chambers and the mechanical wear of the wafer handling equipment. The chances of generating contaminating particles are also increased in process chambers that are equipped with plasma enhancement. Various chemically reacted fragments are generated from the processing gases which include ions, electrons and radicals. These fragments can combine and form negatively charged particles which may ultimately contaminate a substrate that is being processed in the chamber. Various other materials such as polymeric films may also be coated on the process chamber walls during plasma processing. The films may dislodge and fall from the process chamber walls when subjected to mechanical and thermal stresses such that they fall onto the wafers that are being processed.
An example for illustrating chamber wall contamination is the etcher 10 shown in FIG. 1. Etcher 10 is a plasma chamber that is equipped with magnetic field enhancement generated by an upper rotating magnet 12 and a lower rotating magnet 14. The plasma etcher 10 includes a housing 16 that is typically made of a non-magnetic material such as aluminum which defines a chamber 20. A substrate holder 22 which is also a cathode is connected to a RF generator 24 which is in turn connected to a gas inlet (or showerhead) 26. The showerhead 26 also acts as an anode. A process gas 28 is supplied to chamber 20 through the gas inlet 26. A semi-conducting substrate 30 to be processed is positioned on the substrate holder or cathode 22.
The semi-conducting substrate 30 is normally held against the substrate holder 22 by a clamp ring 32. During a plasma etching process, a semi-conducting wafer 30 heats up significantly during the process and must be cooled by a cooling gas from a cooling gas supply (not shown) such that heat can be transferred to a water cooled wafer holder 36. The function of the clamp ring 32 is also to hold the substrate 30 down against the pressure generated by the cooling gas. An exhaust port 34 which is connected to a vacuum pump (not shown) evacuates the chamber. During an etching process, the upper rotating magnet 12 and the lower rotating magnet 14 function together to provide a magnetic field inside the process chamber 20.
In a conventional cleaning process for the plasma etch chamber 10, a cleaning gas supply is first flown through the gas inlet port 26 into the chamber 20 and then, the RF generator 24 is turned on. The cleaning procedure is conducted after a predetermined number, i.e. between 100-500 of wafers have been processed in chamber 20. A plasma of the cleaning gas ions is formed in the space between the showerhead 26 and the wafer holder 32 to loosen the contaminating particles and films from the chamber walls and the showerhead 26 (i.e. the upper electrode).
In an etching process for polysilicon or metal, a chlorine etching gas is frequently used. On the other hand, the etching gas used for oxide or nitride is frequently a fluorine gas. During a plasma etching process, the reactive plasma ions have a high energy level and therefore can easily combine with any available chemical fragments or elements in the chamber to form contaminating particles or films. For instance, in a metal etching process, the elements frequently seen in the etch chamber includes C, H, N, O, Al, Ti, TiN and Si. Different elements such as C, N, O, Br, Si and W are seen in a polysilicon etch chamber. The contaminating particles or films formed by often volatile chemical fragments or elements during an etching process float or suspend in the chamber due to the interaction with high energy plasma ion particles when the RF power is turned on. The phenomenon of the floating or suspended particles can be explained by the fact that the particles have higher energy and temperature while suspended in a plasma cloud. However, at the end of a conventional etching process, the RF power is switched off which leads to the sudden loss of energy in the suspended contaminating particles and causing them to fall or stick to the chamber walls or the upper electrode. This is shown in FIGS. 2A and 2B.
FIG. 2A shows a simplified etch chamber 40 equipped with a chamber cavity 42 defined by chamber walls 44. A process gas inlet 46 is used to flow a process gas into the chamber cavity 42. An upper electrode 48 and a lower electrode/wafer holder 50 are used to supply RF power to the chamber and to produce plasma ions. A gas outlet 54 is used to evacuate the process gas from the chamber cavity 42 at the end of the etching process. During the etching process, contaminating particles 52 formed as etch byproducts are buoyant and are suspended in the chamber cavity 42. A wafer 56 is supported by the wafer holder 50 for processing.
After a conventional etching process is conducted, the RF power and the heating lamps are turned off. The suspended, contaminating byproducts or particles 52 are easily deposited on chamber walls 58, upper electrode 48 and wafer 50. These contaminating particles (or films) are frequently formed of a carbon or chlorine containing polymeric material and when adhered to the chamber wall 58, are very difficult to remove. Conventionally, a wet cleaning process must be conducted after approximately 2,000-4,000 wafers have been processed in the etch chamber 40. The wet cleaning process is carried out by suing cleaning solvent such as IPA, deionized water, combination IPA/deionized water or the more volatile acetone. The wet cleaning process causes a downtime of the etcher as long as one full day.
It has been discovered that a major chamber contamination source is the polymeric material that adhered to the chamber wall during the etching process when the chamber wall is heated to at least 100xc2x0 C. At the end of the etching process, the RF and the heating lamps are turned off which causes the chamber wall, i.e. specifically the top chamber wail, which is frequently formed of a quartz material to cool down rapidly below 100xc2x0 C. The contraction of the polymeric based contaminating particles or films adhered to the top chamber walls causes them to peel off from the chamber wall and fall on a wafer supported in the chamber or on other chamber components causing a serious contamination problem. The cooling of the chamber walls at the end of each etching process when the heating lamps are turned off, thus becomes a major cause of chamber contamination by the polymeric based contaminating particles and films.
It is therefore an object of the present invention to provide a method for preventing contamination in a plasma process chamber that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for preventing contamination in a plasma process chamber that can be carried out by flowing a heated gas onto the chamber wall of the process chamber after heating lamps are turned off at the end of an etching process.
It is a further object of the present invention to provide a method for preventing contamination in a plasma process chamber by heating the chamber interior to at least 80xc2x0 C. by an auxiliary heating system after the main heating system of heating lamps are turned off.
It is another further object of the present invention to provide a method for preventing contamination in a plasma process chamber by turning off heating lamps and simultaneously flowing a heated gas having a temperature of at least 100xc2x0 C. onto the chamber wall for preventing contaminating particles or films from falling off the chamber wall.
It is still another object of the present invention to provide a method for preventing contamination in a plasma process chamber by flowing a gas heated to a temperature between about 100xc2x0 C. and about 150xc2x0 C. onto an exterior surface of a top chamber wall of the process chamber.
It is yet another object of the present invention to provide a method for preventing contamination in a plasma process chamber by utilizing an auxiliary heating system for heating the chamber wall which is turned off when the temperature of the heated gas exceeds 150xc2x0 C.
It is still another further object of the present invention to provide a plasma process chamber that is equipped with an auxiliary heating system for preventing chamber contamination which includes a chamber body, a primary heating system of heating lamps and an auxiliary heating system for heating gases to at least 100xc2x0 C.
It is yet another further object of the present invention to provide a plasma process chamber that is equipped with an auxiliary heating system for preventing chamber contamination wherein the auxiliary heating system generates a heated gas at a temperature between about 100xc2x0 C. and about 150xc2x0 C. for heating the chamber wall of the process chamber such that a temperature of at least 80xc2x0 C. inside the chamber is maintained.
In accordance with the present invention, a method and an apparatus for preventing contamination in a plasma process chamber such as a metal etch chamber are disclosed.
In a preferred embodiment, a method for preventing contamination in a plasma process chamber can be carried out by the operating steps of first providing a plasma process chamber that is equipped with a heating means and a top chamber wall, conducting a plasma process in the plasma process chamber and generating contaminating particles adhered to an interior surface of the top chamber wall, and turning off the heating means and simultaneously flowing a gas heated to at least 100xc2x0 C. onto an exterior surface of the top chamber wall for preventing the contaminating particles from falling off the interior surface of the top chamber wall.
The method for preventing contamination in a plasma process chamber may further include the step of maintaining a temperature inside the plasma process chamber of at least 80xc2x0 C. The method may further include the step of providing the heating lamps as the heating means, or the step of providing the top chamber wall in a quartz material. The method may further include the step of flowing a gas heated to a temperature between about 100xc2x0 C. and about 150xc2x0 C. onto an exterior surface of the top chamber wall, or the step of flowing nitrogen gas heated to at least 100xc2x0 C. onto an exterior surface of the top chamber wall. The method may further include the step of dispersing the gas heated to at least 100xc2x0 C. onto an exterior surface of the top chamber wall. The method may further include the step of heating the gas to at least 100xc2x0 C. by an electric heating means, or heating the gas to at least 100xc2x0 C. by an electric heating means and sensing the gas temperature by a temperature sensor, or the step of shutting off the electric heating means when the gas is heated to a temperature higher than 150xc2x0 C.
The present invention is further directed to a plasma process chamber that is equipped with an auxiliary heating means for preventing chamber contamination which includes a chamber body equipped with a primary heating means, a top chamber wall and an auxiliary heating means mounted to the chamber body for heating the top chamber wall when the primary heating means is turned off such that a temperature inside the chamber body is at least 80xc2x0 C. for preventing contaminating particles adhered to an interior surface of the top chamber wall from falling off.
The plasma process chamber equipped with an auxiliary heating means for preventing chamber contamination may further include an auxiliary heating means that generates a heated gas for heating the top chamber wall, or an auxiliary heating means that generates a heated gas having a temperature of at least 100xc2x0 C. for heating the top chamber wall, or an auxiliary heating means that generated a heated gas that has a temperature between about 100xc2x0 C. and about 150xc2x0 C. for heating the top chamber wall. The heated gas generated by the auxiliary heating means may be a heated nitrogen. The primary heating means may be a plurality of heating lamps. The auxiliary heating means may be electric resistance heaters for heating a gas, the electric heating means may be equipped with a temperature sensor for shutting off the electric heating means when the gas heated exceeds 150xc2x0 C. The plasma process chamber may be a metal etcher. The contaminating particles may be formed of a polymeric material.